Superabsorbent polymers are mainly used as absorbents for biological fluids, water, aqueous solutions and the like. These absorbents are primarily used in diapers, adult incontinence products as well as in feminine hygiene applications. Polyacrylates and polyacrylamides, as well as their copolymers, are among the best known superabsorbents. Alternative acrylic superabsorbent polymer forms, including partially biodegradable materials, are described in “Modern Superabsorbent Polymer Technology” (Buchholz F. L. and Graham A. T. Eds., Wiley-VCH, New York, 1998).
Commercial superabsorbents are mainly polyacrylate-based polymers. However, their biodegradability is questionable, especially for high molecular weight polymers. These polymers are synthesized from monomers such as acrylic acids and acrylamides. Following the polymerization process, there are still residual monomers or oligomers showing toxicity and allergenic potential.
These synthetic polymers have also been grafted onto polysaccharides. Superabsorbent polysaccharide-based grafted-polymers are obtained through the grafting of an unsaturated monomer (acrylonitrile, acrylic acid, acrylamide) onto starch or, less frequently, cellulose. The so-obtained polymers, also called “Super Slurper”, illustrate a water absorption capacity ranging from 700 to 5300 g/g for deionised water, and up to 140 g/g in a 0.9% saline solution (weight by volume of NaCl, referred hereinafter as saline solution) (Riccardo P. O., Water-Absorbent Polymers: A Patent Survey. J. Macromol. Sci., Rev. Macromol. Chem. Phys., 1994, 607-662 (p.634) and cited references). Despite their high water absorption capacity, these grafted polysaccharides, prepared by radical polymerization, are hypoallergenic and are not known to be biodegradable.
Among other polymers, polyaspartates have been recognized as offering good absorbent properties and as being biodegradable (Ross et al., U.S. Pat. No. 5,612,384). However, polyaspartates appear to have several drawbacks regarding their low molecular weight. Furthermore, polyaspartates are produced synthetically (Koskan et al., U.S. Pat. No. 5,221,733) from non-renewable sources such as for example maleic anhydride (obtained from butane). Finally, these polymers are strongly ionic and subject to performance fluctuations in saline solutions.
Polymeric blends and mixtures, used as absorbents or superabsorbents, are known. More specifically, the synergistic effect on the absorption against pressure of two synthetics polyacrylate-based hydrogel-forming particles has been reported (Schmid et al., EP 0 691 133 A1). Since these formulations comprise synthetic polymers, they are unsuitable in light of allergenic, abrasive, ecological or toxicological concerns.
Chmelir and Klimmek (U.S. Pat. No. 5,340,853), teach a synergistic absorbing and swelling agent consisting of at least two components. The agent is made from a water-swellable synthetic polymer or copolymer, crosslinked with a multifunctional compound, and a second component. The second component is a polysaccharide such as galactomannans or polygalactomannans. Alternatively, it could comprise admixtures of a galactomannan or polygalactomannans with other natural or synthetic polymers such as starch and modified starch. Even though the inventors refer to a synergistic effect when mixing the two components, no clear evidence for the synergy has been demonstrated when only polysaccharide components are used. Furthermore, since these formulations require synthetic polymers, such as polyacrylates, they are unsuitable for many uses in light of allergenic, abrasive, ecological or toxicological concerns.
Many other polyacrylate-polysaccharide based synergistic compositions have been disclosed such as those taught by Gunther, Klimmek, Brüggeman and Chmelir (U.S. Pat. Nos. 5,721,295; 5,847,031; 5,736,595; 5,264,471; and 4,693,713 Reissue 33,839). However, since these formulations again require synthetic polymers, such as polyacrylates, they are unsuitable in light of allergenic, abrasive, ecological or toxicological concerns.
Renewable resources such as mixtures of polysaccharides have also been considered as absorbent materials. U.S. Pat. No. 5,801,116, granted to Rhodia Inc. (Cottrell et al.) discloses one or more polysaccharides having a particle size of greater than 200 mesh (74 microns), preferably modified guar gum. This modified guar gum may be used alone as an absorbent material or in combination with other known materials, such as natural or synthetic hydrophilic polymers. The inventors describe a potential synergistic absorbency when the compositions are combined with one or more of several classes of chemicals including simple carbohydrates (glucose, fructose, sorbitol, and the like) and synthetic hydrophilic polymers. However, no specific composition is exemplified to prove the synergistic hypothesis. Furthermore, these guar absorbents have an undesirable tendency to give an syneresis effect (referred as slimy effect) to the wearer.
U.S. Pat. No. 4,454,055 (Richman et al.), issued to National Starch, teach synergistic interactions between ionically crosslinked polyelectrolytes (polyacrylates-starches), and modified starches or other extenders. Because these ionically crosslinked polyelectrolytes are made mainly from synthetic SAPs (Super Absorbent Polymers), they are again unsuitable for many uses in light of allergenic, abrasive, ecological or toxicological concerns.
Polysaccharide-protein synergies have also been reported in the food industry. The synergistic compositions relate to the viscosity or texture enhancement of food gels (Alloncle M et al., Cereal Chemistry, 66 (2), 1989, pp. 90-93; Kaletung-Gencer G et al., Journal of Texture Studies, 17 (1), 1986, pp. 61-70; Alloncle M et al., Food Hydrocolloids, 5 (5), 1991, pp.455-467; Sudhakar V et al., Food Chemistry, 55 (3), 1996, pp. 259-264; Rayment P et al., Carbohydrate polymers, 28 (2), 1995, pp. 121-130; Pellicer J et al., Food Science and Technology International, 6 (5), 2000, pp. 415-423; Tako M, Bioscience Biotechnology and Biochemistry, 56 (8), 1992, pp. 1188-1192; Tako M et al., Agricultural and Biological Chemistry, 52 (4), 1988, pp.1071-1072; Murayama A et al., Bioscience, Biotechnology and Biochemistry, 59 (1), 1995, pp. 5-10; Goycoolea F. M et al., Gums and stabilizers for the food industry 7: proceedings of the 7th international conference in Wrexham, July, 1993, pp. 333-344). The reasons for being of these food gels is different when compared to those used in hygiene applications. Food gels aren't designed to absorb or retain large amounts of saline or physiological fluids under pressure. Indeed, no synergistic effects have been reported in these publications concerning absorbent or superabsorbent technologies.
Glass-like, pregrelatanized starches, have been disclosed by Groupe Lysac (Huppé et al. C A U.S. Pat. No. 2,308,537) as being a useful absorbent for liquids. However, these pregelatinized starches only absorb 8 g/g, which is too low to be useful in the hygiene industry. In order to improve the absorption capacity of these modified starches, they were mixed with xanthan and guar gums. The modified starches have also been blended in mixtures with sodium carboxymethyl cellulose (CMC). Some synergistic effects were observed but only in those cases where starches were admixed with specific concentrations of guar and xanthan gums. Moreover, the disclosed absorption capacities remained too low to be useful in the hygiene industry.
There thus remains a need for novel synergistic compositions of polysaccharides with improved performance as natural and biodegradable absorbent materials or superabsorbents.
The present invention seeks to meet these and other needs.
The present invention refers to a number of documents, the content of which is herein incorporated by reference in their entirety.